Mac brew 安装 MySQL 和 MariaDB 的默认密码，解决无法登陆问题

苹果电脑 Mac brew 安装 MySQL 和 MariaDB 后，默认下面的命令是无法登陆的

mysql -u root

输出结果如下

ERROR 1698 (28000): Access denied for user 'root'@'localhost'

一般情况下，这是缺少密码，但是我们并不知道密码是什么啊

mysql -uroot -p

输出结果如下

Enter password: 
ERROR 1698 (28000): Access denied for user 'root'@'localhost'

安装的时候也没啥提示啊

==> Downloading https://homebrew.bintray.com/bottles/mariadb-10.4.6.high_sierra.bottle.tar.gz
==> Downloading from https://akamai.bintray.com/b4/b4466c2e19ab1e71f29f1b2a864869840c1ad1ff3c37a4e7a68573d503d30a00?__gda__=exp=156405
######################################################################## 100.0%
==> Pouring mariadb-10.4.6.high_sierra.bottle.tar.gz
==> /usr/local/Cellar/mariadb/10.4.6/bin/mysql_install_db --verbose --user=yufei --basedir=/usr/local/Cellar/mariadb/10.4.6 --datadir=
==> Caveats
A "/etc/my.cnf" from another install may interfere with a Homebrew-built
server starting up correctly.

MySQL is configured to only allow connections from localhost by default

To connect:
    mysql -uroot

To have launchd start mariadb now and restart at login:
  brew services start mariadb
Or, if you don't want/need a background service you can just run:
  mysql.server start
==> Summary
????  /usr/local/Cellar/mariadb/10.4.6: 745 files, 179.3MB

好吧，没办法了

经过千辛万苦，终于在 MariaDB 的官网上找到答案了

In this case, the following defaults apply:

The host name is localhost.
The user name is either your Unix login name, or ODBC on Windows.
No password is sent.
The client will connect to the server, but not any particular database on the server.

大概的意思是说，默认情况下， MariaDB 的默认 host 是 localhost，默认的登陆用户名是电脑的登陆用户名，也就是开机的登陆用户名，比如我的是 yufei，默认的密码是空的。

于是，登陆就改成了下面这个

mysql -u yufei

输出结果如下

Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 12
Server version: 10.4.6-MariaDB Homebrew

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

哈哈，终于连接上了。